fix(agent-core): suppress the spurious error event for step-capped goal turns

[chengluyu]

Related Issue

Follow-up to #2210 (which made goal pursuit continue across the per-turn step limit). The problem is explained below.

Problem

After #2210, a goal turn that hits loop_control.max_steps_per_turn no longer pauses the goal — but the TUI still renders a red, actionable error banner for every capped turn:

Error: [loop.max_steps_exceeded] Turn exceeded maxSteps=3. …
If this persists, run '/export-debug-zip' and share the file with us for diagnosis.

Root cause: runOneTurn's catch path emits a standalone error event for any failed turn (in addition to turn.ended{reason:'failed'} and the turn.interrupted{reason:'max_steps'} loop event). The TUI's session-error handler renders that event as an actionable failure. For goal-driven turns the cap is expected control flow — the driver immediately starts the next continuation turn — so the banner is pure noise that makes an intentional limit look like a malfunction.

What changed

• In v1 TurnFlow.runOneTurn, the standalone error event is no longer emitted when the failure is loop.max_steps_exceeded and a goal is active (i.e. exactly the turns the goal driver will continue). Everything else is preserved: turn.ended{reason:'failed', error:…}, the turn.interrupted{reason:'max_steps'} loop event, the StopFailure hook, and API-error telemetry.
• Ordinary (non-goal) turns still emit the standalone error event — a user's prompt cut by the cap must keep surfacing.
• Tests: the v1 goal harness test now asserts capped goal turns produce zero standalone error events; the existing non-goal max-steps test now asserts the event is still emitted (right after turn.ended).
• Includes a changeset (@moonshot-ai/kimi-code, patch).

Checklist

• I have read the CONTRIBUTING document.
• I have linked a related issue, or explained the problem above.
• I have added tests that prove my feature works.
• Ran gen-changesets skill, or this PR needs no changeset.
• Ran gen-docs skill, or this PR needs no doc update.

[changeset-bot]

🦋 Changeset detected

Latest commit: aefbc7f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@moonshot-ai/kimi-code	Patch

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[pkg-pr-new]

pnpm dlx https://pkg.pr.new/@moonshot-ai/kimi-code@aefbc7f

npx https://pkg.pr.new/@moonshot-ai/kimi-code@aefbc7f

commit: aefbc7f